1. Field of the Invention
The present invention relates to a peer-to-peer (P2P) type information distribution system having a plurality of nodes capable of performing communication with each other via a network. The invention relates to an information distribution system or the like in which at least one piece of distribution information is copied and stored into a plurality of nodes and, more particularly, to the technical field for managing node information indicative of nodes storing the copied distribution information.
2. Discussion of the Related Art
There is known a method of increasing resistance to a failure and dispersibility of accesses by preparing a plurality of pieces of replica information (hereinbelow, called replicas) for one piece of distribution information (for example, content data) in a peer-to-peer information distribution system of this kind and dispersedly disposing (dispersedly storing) the replica information in a plurality of nodes participating in the system.
As a proposal related to generation and allocation of such replicas, for example, patent document 1 discloses a method of generating and allocating replicas in a balanced manner in an entire network in a service group by referring to the whole size (whole information amount) and the number of replicas existing in devices connected in the service group on the network. Patent document 2 discloses a method of dynamically generating replicas in accordance with an access frequency.
In an information distribution system using a distributed hash table (hereinbelow, DHT) as disclosed in non-patent document 1, a node (hereinbelow, called “root node”) that manages, as index information, node information (for example, including an IP address and a port number of a content holding node) indicative of a node in which a replica is stored (hereinbelow, called “content holding node”) is determined every content data (that is, a root node exists for each content). A node desiring to obtain content data inquires the root node for node information of a node that stores a replica of the content data.    Patent Document 1: Japanese Patent Application Laid-Open No. 2003-99337    Patent Document 2: Japanese Patent Application Laid-Open No. 2003-216521    Non-Patent Document 1: “Lightweight Load Balancing for Distributed Hash Tables”, The Institute of Electronics Information and Communication Engineers, Technical Report